A method presently utilised for the manufacture of such screens, involves the construction of a tubular cage of supporting rods, about which screening wires are wound and welded at their intersections with the support rods. The screen wires are of generally triangular cross section, with the apex of the wires contacting the support rods giving a line contact therewith suitable for electric welding.
In this prior art method, the welded tube is then split longitudinally and flattened, and cut into four trapezoidal sections and four rectangular sections. These sections are then rolled in the opposite direction so that the screening wires are then on the inside of the curved surface. The trapezoidal and rectangular sections are then welded along adjacent edges with the aid of interposed connecting strips to make an imperfect frusto-conical screen. Support rings are then welded at the ends of the screen.
This technique gives an adequate weld strength, which is necessary for the screen to have a life which is limited in most cases only by wear of the screening rods, but since the cross section of the screen insufficiently approaches that of a perfect frusto-conical surface, the screen is not perfectly balanced, leading to uneven wear resulting in premature failure of the basket, and wear on the bearings and associated machinery. Furthermore, this method of fabrication is very time consuming, and therefore very costly.